This invention relates to antibiotic susceptibility testing and more particularly a test assembly of a series of hollow cups in which cups are placed various concentrations of various antibiotics or other therapeutic control agents to ascertain the interaction between such control agents and various microorganisms, usually pathogenic. With the proliferation of antiobiotics and other drugs both in the hospital and in the laboratory as well as educational institutions there is an increasing demand for information concerning the susceptability or sensitivity of a particular microorganism to various antibiotics or drugs.